Micromechanical Device for Measuring an Acceleration, a Pressure or the Like and a Corresponding Method

ABSTRACT

A micromechanical device measures an acceleration, a pressure or the like. It comprises a substrate having at least one fixed electrode, a seismic mass moveably arranged on the substrate, at least one ground electrode, which is arranged on the seismic mass, and resetting means for returning the seismic mass into an initial position, wherein the fixed electrode and the ground electrode are configured in one measurement plane for measuring an acceleration, a pressure or the like in the measurement plane, and wherein the fixed electrode and the ground electrode are configured for measuring an acceleration, pressure or the like acting on the seismic mass perpendicular to the measurement plane. The disclosure likewise relates to a corresponding method and a corresponding use.

The invention relates to a micromechanical device for measuring anacceleration, a pressure or the like and to a corresponding method and acorresponding use.

PRIOR ART

Acceleration sensors are used in many areas. In recent times, forexample, they have frequently been used in mobile telephones in order todetect a change in the attitude of the mobile telephone. If the mobiletelephone is rotated in one plane by a user, for example, in order to beable to use the conventionally rectangular display transversely ratherthan longitudinally, this is detected by a corresponding accelerationsensor and forwarded to the operating system of the mobile telephone.The latter then calculates the changed attitude of the mobile telephoneby using the acceleration measured by the acceleration sensor andmatches the screen content to the calculated new attitude by means of acorresponding rotation of the screen content, so that a user can alsosee the screen content of the mobile telephone transversely in thedesired way.

In addition, acceleration sensors are also used in hard drives in orderto avoid damage to the hard drive. For instance, the acceleration sensordetects when the hard drive is inadvertently dropped by a user duringthe installation of the hard drive in a computer. The accelerationsensor then measures a free fall of the hard drive and the hard drivemoves a read/write head of the hard drive into a secure parking positionas a precaution, so that, in the case of the drop heights that usuallyoccur, no damage is caused to the hard drive by the read/write head whensaid hard drive strikes the floor.

An acceleration can, for example, be determined by means of acapacitance change. For this purpose, interengaging finger electrodesare arranged in a common plane on a seismic mass and on a base. Theseismic mass is mounted in this case such that it can move with respectto the base. The finger electrodes of the seismic mass and thecorresponding finger electrodes of the base form capacitances betweenthe respective electrodes. By using a change in the capacitances, thecorresponding deflection of the seismic mass in the x or y direction inthe plane of the finger electrodes can then be measured and thereforethe force, acceleration, pressure, etc. acting on the seismic mass canbe determined.

US 2005/0092107 A1 has disclosed a device for measuring an accelerationin two dimensions, a deflection in the third dimension being compensatedfor. The measurement of an acceleration in the x and/or y direction iscarried out by means of interengaging finger electrodes of a seismicmass and a substrate. In order to compensate for an acceleration orforce on the seismic mass perpendicular to the x-y plane, the fingerelectrodes of the substrate are arranged such that they can moveperpendicular to the x-y plane. Then, if the seismic mass experiences aforce with a component perpendicular to the x-y plane, the seismic massis correspondingly displaced in the z direction, i.e. perpendicular tothe x-y plane. The finger electrodes of the substrate, which arearranged such that they can move, are rotated in a corresponding way bythe force acting in the z direction. Overall, therefore, the capacitancebetween the finger electrodes of the seismic mass and the fingerelectrodes of the substrate does not change on account of the likewisedeflecting finger electrodes of the substrate. Therefore, a forcecomponent acting in the z direction is compensated for.

In order to be able to measure an acceleration perpendicular to the x-yplane, it is known to the applicant from a further reference to form theseismic mass as a rocker. An additional electrode can then be arrangedon the seismic mass, parallel to the x-y plane on one side of theseismic mass, and likewise an additional electrode can be arranged in acorresponding way on the substrate, perpendicular to and at a distancefrom the x-y plane, so that these form a capacitance, which changes inthe event of a deflection of the seismic mass perpendicular to the x-yplane. By using this change, the corresponding accelerationperpendicular to the x-y plane is then determined. However, thisrequires a complicated construction of the substrate and of the seismicmass and makes the corresponding acceleration sensor more expensive.

DISCLOSURE OF THE INVENTION

The micromechanical device defined in claim 1 for measuring anacceleration, a pressure or the like comprises a substrate having atleast one stationary electrode, a seismic mass arranged such that it canmove on the substrate, at least one ground electrode, which is arrangedon the seismic mass, wherein the stationary electrode and the groundelectrode are configured in a measuring plane to measure anacceleration, a pressure or the like in the measuring plane, and whereinthe stationary electrode and the ground electrode are configured tomeasure an acceleration, a pressure or the like acting on the seismicmass perpendicular to the measuring plane.

The method defined in claim 9 for measuring an acceleration, a pressureor the like, in particular suitable to be implemented by a device asclaimed in at least one of claims 1 to 7, comprises the steps ofarrangement of at least one stationary electrode on a substrate and atleast one ground electrode on a seismic mass arranged such that it canmove on the substrate, wherein the stationary electrode and the groundelectrode interact to measure an acceleration, a pressure or the like ina measuring plane, action of an external force on a seismic massperpendicular to the measuring plane, deflection of the seismic mass onaccount of the external force in a direction perpendicular to themeasuring plane, measurement of a change in a capacitance between the atleast one ground electrode and the at least one stationary electrode,and determination of the acceleration, the pressure or the like by usingthe measured change in the capacitance.

In claim 10, a use of a device as claimed in at least one of claims 1 to8 for measuring an acceleration and/or a pressure is defined.

ADVANTAGES OF THE INVENTION

The micromechanical device defined in claim 1 for measuring anacceleration, a pressure or the like, and the corresponding methoddefined in claim 8 have the advantages that electrodes already arranged,which measure an acceleration or a pressure in an x-y plane, cantherefore also be used in a simple way to measure an acceleration, apressure or the like in a direction perpendicular to the x-y plane. As aresult, additional electrodes which measure an acceleration in a zdirection, i.e. a direction perpendicular to the x-y plane, aredispensed with. At the same time, the device can also be produced simplyand the method can be carried out simply, since the complicatedarrangement of additional electrodes on the substrate and on the seismicmass and the shaping of the substrate z direction as well can bedispensed with completely.

Further features and advantages of the invention are described followingsubclaims.

According to an advantageous development, the seismic mass is formedsuch that it can rotate about an axis of rotation, wherein the axis ofrotation is arranged in the measuring plane. The advantage achievedthereby is that, firstly, complicated resetting of the seismic mass intoan initial position can therefore be dispensed with, since appropriatemeans can be provided centrally. Secondly, a simple option fordeflection perpendicular to the measuring plane is therefore alsoprovided.

According to a further advantageous development, the stationaryelectrode and ground electrode are configured to form at least twocapacitances between stationary electrode and ground electrode. Theadvantage achieved in this case is that a direction of the deflectionperpendicular to the x-y plane can therefore be determined in a reliableway. In the event of an appropriate deflection, the magnitude of thefirst capacitance decreases, whereas the magnitude of the secondcapacitance increases. If a deflection takes place in the oppositedirection, the magnitude of the first capacitance increases, whereas themagnitude of the second capacitance increases.

According to a further advantageous development of the invention, thestationary electrode comprises at least two metallic first regions, andthe ground electrode comprises at least one metallic second region,wherein the first and second metallic regions interact to form the atleast two capacitances. Therefore, in a simple and inexpensive way, theformation of two capacitances for the detection of the direction of thedeflection of the seismic mass perpendicular to the measuring plane ismade possible. If the first and/or second metallic regions are arrangedone above another on the respective electrode in the directionperpendicular to the measuring plane, the measurement of the force, theacceleration, the pressure or the like can be carried out still morereliably, and at the same time the direction of the deflectionperpendicular to the x-y plane can be determined.

According to a further advantageous development of the invention, onopposite sides of the seismic mass in relation to the axis of rotation,in each case at least one ground electrode is arranged on the seismicmass and in each case at least one stationary electrode is arranged onthe substrate. In this way, the reliability of a measurement of apressure, an acceleration or the like is increased further, since aplurality of electrodes is then available on various sides to measure adeflection in the z direction.

According to a further advantageous development of the invention, ineach case the upper first regions of a first stationary electrode arerespectively interconnected with the lower first regions of a secondstationary electrode for measuring an acceleration, a pressure or thelike. Such an arrangement permits a considerable reduction in thetransverse sensitivity of the device. If the seismic mass is deflectedin the z direction, then, if it is mounted such that it can rotate abouta central axis, it experiences a positive deflection on one side of theaxis of rotation and a corresponding negative deflection on the otherside of the axis of rotation perpendicular to the measuring plane. Thepositive and negative deflection can then be determined and, by means ofdifferentiation of the respective measured changes in the capacitances,possible interference can be eliminated.

According to a further advantageous development of the invention, thefirst and/or second metallic regions each comprise at least two metallayers arranged one above another, which are connected to one anotherelectrically, in particular by means of through contacts. The advantagehere is that conventional CMOS production methods can therefore be used,which are able to provide appropriate metallic regions or metal layers,firstly inexpensively and secondly reliably.

According to a further advantageous development of the invention, thestationary electrode and/or the ground electrode comprise/s at least onedeposited, in particular dielectric, layer. The advantage achieved hereis that the electrodes can therefore be produced in a simple andinexpensive way and, at the same time, the metallic regions can beinsulated from one another and also the metal layers forming themetallic regions can be insulated from one another.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention can be gathered fromthe following description of exemplary embodiments. Here:

FIG. 1 shows a stationary electrode and a ground electrode of a deviceaccording to one embodiment of the present invention;

FIG. 2 shows a schematic representation of a device according to theembodiment of FIG. 1 in plan view of an x-y plane;

FIG. 3 shows stationary electrodes and ground electrodes of a deviceaccording to the embodiment of FIG. 1; and

FIG. 4 shows steps of a method according to one embodiment of thepresent invention.

EMBODIMENTS OF THE INVENTION

FIG. 1 shows a stationary electrode and a ground electrode of a deviceaccording to one embodiment of the present invention.

In FIG. 1, designation 1 designates a stationary electrode, which isarranged on a substrate S (not shown in FIG. 1). The stationaryelectrode 1 is configured substantially as a finger electrode 1 a and isillustrated in cross section in FIG. 1. In the end region of thestationary electrode 1, the latter has layers 5 a-5 e of dielectrics 5arranged one above another. Five layers 5 a-5 e are shown in FIG. 1. Thefirst layer 5 a from bottom to top according to FIG. 1 comprises onlyone dielectric 5. The second layer 5 b arranged over the first layer 5 acomprises, in the lower region on the left and right of an axis ofsymmetry M of the stationary electrode 1, a metal layer 12 b which isconnected via a through contact 13 to a metal layer 12 a of the adjacentthird layer 5 c. This metal layer structure comprising metal layers 12a, 12 b and through contact 13 is respectively arranged in the regionboth of the left-hand and also of the right-hand edge of the stationaryelectrode 1 and symmetrically with respect to the axis of symmetry M.The third layer 5 c—as explained above—comprises only the lower metallayer 12 a.

Further layers 5 d, 5 e, which correspond substantially in structure tothe first and second layer 5 a, 5 b, are stacked on the third layer 5 c.In this way, an upper first and a lower first metallic region 3 a, 4 aare arranged on the stationary electrode 1, respectively on the left andright of the axis of symmetry M, each comprising two metal layers 12 a,12 b which are connected by means of at least one through contact 13.

On the right in FIG. 1, the ground electrode 2, which is arranged on aseismic mass 10 (not shown in FIG. 1), is now shown in cross section.This is likewise formed as a finger electrode 2 a. The seismic mass 10and therefore the ground electrode 2 is arranged such that it can movein the vertical direction relative to the stationary electrode 1 in thedirection R according to FIG. 1. The structure of the ground electrode 2corresponds substantially to the structure of the stationary electrode 1according to FIG. 1. In contrast to the stationary electrode 1, however,only two metal layers 12 a, 12 b are arranged in the third and fourthlayer 5 c, 5 d. These are once more connected to one another via throughcontacts 13. In this way, by means of the two metal layers 12 a, 12 band the through contact 13 connecting the latter, a second metallicregion 6 is formed.

Two capacitances C₁, C₂ are formed between the second metallic region 6of the ground electrode 2 and the two first metallic regions 3 a, 4 a ofthe stationary electrode 1. The first capacitance C₁ is formed betweenthe upper metallic first region 3 a and the second metallic region 6,the second capacitance C₂ is formed between the lower first metallicregion 4 a and the second metallic region 6 of the ground electrode 2.If then, as indicated in FIG. 1, the ground electrode 2 is displaced ordeflected upward in the direction R with respect to the stationaryelectrode 1, the capacitance C₁ rises on account of the distance betweenthe upper first metallic region 3 a of the stationary electrode 1 andthe second metallic region 6 of the ground electrode 2 becoming smaller,whereas the capacitance C₂ decreases on account of the distance betweenthe lower first metallic region 4 a of the stationary electrode 1 andthe second metallic region 6 of the ground electrode 2 becoming larger.In an initial position, the stationary electrode 1 and the groundelectrode 2 are arranged in such a way that the respective capacitancesC₁ and C₂ are equal: C₁=C₂.

Both the stationary electrode 1 and/or the ground electrode 2 comprise/slayers 5 a-5 e arranged one above another, as explained above. Thisstack of layers 5 a-5 e can be produced, for example, by depositing theindividual layers 5 a-5 e after and on one another. Furthermore, thestationary electrode 1 and/or the ground electrode 2 can also comprise aregion of a semiconductor substrate, for example silicon.

FIG. 2 shows a schematic representation of a device according to theembodiment of FIG. 1 in plan view of an x-y plane.

In FIG. 2, designation S designates a substrate on which a plurality ofelectrode fingers 1 a of a stationary electrode 1 is arranged. Betweenthe respective electrode fingers 1 a, corresponding electrode fingers 2a of a ground electrode 2 engage which, according to FIG. 2, arearranged on the left-hand side of a housing 9 for a seismic mass 10. Onthe right-hand side of the housing 9 according to FIG. 2, there arearranged corresponding electrode fingers 2 b, which engage in electrodefingers 1 b of the substrate S. The respectively adjacent electrodefingers 1 a, 2 a and 1 b, 2 b form respectively correspondingcapacitances C₁-C₄, the change in which during a relative movement ofthe electrode fingers 1 a, 1 b and 2 a, 2 b in relation to one anotheris used to measure the force, acceleration, etc. acting on the seismicmass 10.

The housing 9 for the seismic mass 10 is mounted such that it can rotateabout an axis of rotation 11, the axis of rotation being arranged in thex-y measuring plane E and on the substrate S. The seismic mass 10 isarranged asymmetrically in the housing 9 and/or with respect to the axisof rotation 11. On the right-hand side according to FIG. 1, the housing9 has the seismic mass 10, whereas no seismic mass is arranged on theleft-hand side in the housing 9. Furthermore, a resetting means 15 inthe form of a torsion spring is arranged, in order, if appropriate, toset the seismic mass 10 back into its initial position from a deflectionperpendicular to the x-y measuring plane.

FIG. 3 shows stationary electrodes and ground electrodes of a deviceaccording to the embodiment of FIG. 1.

In FIG. 3, an interconnection V₁, V₂, V_(1′) of the first and secondmetallic regions 3 a, 3 b, 4 a, 4 b, 6 a, 6 b of the stationaryelectrode fingers 1 a and 1 b and also of the ground electrode fingers 2a, 2 b is shown in schematic form. In FIG. 3, the stationary electrode 1a, the ground electrode 2 a, the ground electrode 2 b and the stationaryelectrode 1 b are arranged from left to right. The stationary electrode1 b has a corresponding structure as described in FIG. 1, i.e. an upperfirst metallic region 3 a and a lower first metallic region 4 a on theright-hand side of the electrode 1 a. Accordingly, the stationaryelectrode 1 b has, on its left-hand side, i.e. on its side facing thesecond ground electrode 2 b, an upper first metallic region 3 b and alower first metallic region 4 b. For the purpose of differentialevaluation of capacitance changes of capacitances C₁-C₄, the respectiveupper first metallic region 3 a, 3 b of the stationary electrode 1 a isinterconnected with the respective lower first metallic region 4 a, 4 bof the opposite stationary electrode 1 b. These interconnections areillustrated in FIG. 3 as broken lines and designated by the designationsV₁ and V_(1′). The second metallic regions 6 a and 6 b of the groundelectrodes 2 a, 2 b are likewise interconnected with each other,indicated by the broken line V₂ in FIG. 3. In this way, a differentialevaluation of the change in the respective capacitances C₁-C₄ ispossible.

If an external force acts on the seismic mass 10, the ground electrode 2a is displaced upward, for example, and in a corresponding way theground electrode 2 b is displaced downward. In the process, thecapacitance C₁ increases and so does the capacitance C₄, since therespective distance between the first and second metallic regions 3 a, 4b, 6 becomes smaller. At the same time, the capacitance C₂ and C₃decreases, since the distance between the corresponding first and secondmetallic regions 3 b, 4 a, 6 becomes larger. By means of theinterconnection V₁, V_(1′), V₂, the formation of a difference betweenthe increasing capacitances C₁, C₄ and the decreasing capacitances C₂,C₃ is possible; this increases the measurement accuracy.

The respective thicknesses of the dielectric layers 5 a-5 e of thestationary electrode 1 and of the ground electrode 2 are at most 10 μm,preferably less than 5 μm, advantageously between 1 and 2 μm. The firstand second metallic regions 3 a, 3 b, 4 a, 4 b substantially have athickness less than 2.5 μm, preferably less than 1.5 μm, in particularbetween 0.5 and 1 μm. The distance G between a stationary electrode 1and a ground electrode 2 is less than 5 μm, preferably between 1 and 3μm. A metallic region 3 a, 3 b, 4 a, 4 b has an extent perpendicular tothe drawing plane according to FIG. 1 between 10 μm and 500 μm,preferably between 50 μm and 200 μm. An overall height H of thedielectric layers 5 and the metallic regions 3 a, 3 b, 4 a, 4 b, 6 isbetween 3 and 10 μm, preferably between 4 and 8 μm.

FIG. 4 shows steps of a method according to one embodiment of thepresent invention.

The method for measuring an acceleration, a pressure or the like, inparticular suitable to be implemented by a device as claimed in at leastone of claims 1-7, according to FIG. 4 comprises the steps: arrangementS₁ of at least one stationary electrode 1 on a substrate S and at leastone ground electrode 2 on a seismic mass 10 arranged such that it canmove on the substrate S, wherein the stationary electrode 1 and theground electrode 2 interact to measure an acceleration, a pressure orthe like in a measuring plane E, action S₂ of an external force on aseismic mass perpendicular to the measuring plane, deflection S₃ of theseismic mass 10 on account of the external force in a direction Rperpendicular to the measuring plane E, measurement S₄ of a change in acapacitance C₁, C₂ between the at least one ground electrode 2 and theat least one stationary electrode 1, and determination S₅ of theacceleration, the pressure or the like by using the measured change inthe capacitance C₁, C₂.

Although the present invention has been described above by usingpreferred exemplary embodiments, it is not restricted thereto but can bemodified in numerous ways.

1. A micromechanical device for measuring an acceleration, a pressure orthe like, comprising: a substrate having at least one stationaryelectrode; a seismic mass configured to move on the substrate; and atleast one ground electrode supported on the seismic mass, wherein the atleast one stationary electrode and the at least one ground electrode areconfigured in a measuring plane to measure an acceleration, a pressureor the like in the measuring plane, and wherein the at least onestationary electrode and the at least one ground electrode areconfigured to measure an acceleration, a pressure or the like acting onthe seismic mass perpendicular to the measuring plane.
 2. Themicromechanical device as claimed in claim 1, wherein: the seismic massis configured to rotate about an axis of rotation, and the axis ofrotation is defined in the measuring plane.
 3. The micromechanicaldevice as claimed in claim 2, wherein the at least one stationaryelectrode and the at least one ground electrode are configured to formdefine at least two capacitances between the at least one stationaryelectrode and the at least one ground electrode.
 4. The micromechanicaldevice as claimed in claim 3, wherein: the at least one stationaryelectrode includes at least two metallic first regions, the at least oneground electrode includes at least one metallic second region, and theat least two metallic first regions and the at least one metallic secondregion interact to define the at least two capacitances.
 5. Themicromechanical device as claimed in claim 4, wherein: the seismic masshas a first side and a second side opposite the first side in relationto the axis of rotation, at least one first ground electrode of the atleast one ground electrode is supported on the first side of the seismicmass, and at least one second ground electrode of the at least oneground electrode is supported on the second side of the seismic mass,and at least one first stationary electrode of the at least onestationary electrode is supported on a first side of the substratecorresponding to the first side of the seismic mass and at least onesecond stationary electrode of the at least one stationary electrode issupported on a second side of the substrate corresponding to the secondside of the seismic mass.
 6. The micromechanical device as claimed inclaim 5, wherein: upper first metallic regions of the at least one firststationary electrode are respectively interconnected with lower firstmetallic regions of the at least one second stationary electrode formeasuring an acceleration, a pressure or the like.
 7. Themicromechanical device as claimed in claim 4, wherein: at least one ofthe first and second metallic regions include at least two metal layersarranged one above another, and the two metal layers are connected toone another electrically by through contacts.
 8. The micromechanicaldevice as claimed in claim 1, wherein: at least one of the at least onestationary electrode and the at least one ground electrode includes atleast one deposited dielectric layer.
 9. A method for measuring anacceleration, a pressure or the like, comprising: arranging at least onestationary electrode on a substrate and at least one ground electrode ona seismic mass such that the seismic mass is movable on the substrate,wherein the at least one stationary electrode and the at least oneground electrode are configured to interact to measure an acceleration,a pressure or the like in a measuring plane; subjecting the seismic massto an external force perpendicular to the measuring plane; deflectingthe seismic mass on account of the external force in a directionperpendicular to the measuring plane; measuring a change in acapacitance between the at least one ground electrode and the at leastone stationary electrode; and determining the acceleration, the pressureor the like by using the measured change in the capacitance. 10.(canceled)